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Abstract:

A projection display apparatus includes an image projecting unit
projecting an image, an operation unit as an operation device whose
output value changes depending on the amount of operation, a correction
amount setting unit changing a keystone correction amount in accordance
with an output value of the operation unit, and a keystone correcting
unit performing keystone correction on an image to be projected in
accordance with the keystone correction amount. A zero reference position
in which the keystone correction amount is zero is set in an operation
range of the operation unit. The correction amount setting unit sets a
dead zone in the operation range such that the dead zone includes the
zero reference position and an area surrounding this position, and sets
the keystone correction amount to zero in accordance with the output
value corresponding to the inside of the dead zone.

Claims:

1. A projection display apparatus comprising: an image projecting unit
that projects an image; an operation unit whose output value changes
depending on the amount of operation; a correction amount setting unit
that changes a keystone correction amount in accordance with an output
value of the operation unit; and a keystone correcting unit that performs
keystone correction on an image to be projected in accordance with the
keystone correction amount, wherein a zero reference position in which
the keystone correction amount is zero is set within an operation range
of the operation unit, a dead zone, which includes the zero reference
position and an area surrounding the zero reference position is set
within the operation range of the operation unit, and the correction
amount setting unit sets the keystone correction amount to zero in
accordance with the output value corresponding to the inside of the dead
zone.

2. The apparatus according to claim 1, wherein the operation unit
includes a sliding or rotary variable resistor and allows the variable
resistor to change an output voltage in accordance with the operation
amount, and the correction amount setting unit sets the keystone
correction amount to zero in accordance with the output voltage within a
voltage range corresponding to the dead zone.

3. The apparatus according to claim 1, wherein the operation unit is a
sliding operation device capable of being operated in a direction
orthogonal to a projection direction in which an image is projected by
the image projecting unit, and the correction amount setting unit sets a
keystone correction amount in the direction orthogonal to the projection
direction.

4. The apparatus according to claim 1, wherein the projection display
apparatus performs keystone correction without providing information
regarding the keystone correction amount to a user.

5. The apparatus according to claim 1, further comprising: a filter that
performs pixel interpolation on the image, wherein if the output value
corresponds to the inside of the dead zone, the filter does not perform
pixel interpolation, and if the output value corresponds to the outside
of the dead zone, the filter performs pixel interpolation.

6. The apparatus according to claim 1, wherein the operation unit
provides a click state at a specific operation position within the dead
zone.

7. The apparatus according to claim 6, wherein the operation unit
provides the click state at the zero reference position.

8. A method of controlling a projection display apparatus that projects
an image, the apparatus including an operation unit whose output value
changes depending on the amount of operation, the method comprising:
changing a keystone correction amount in accordance with an output value
of the operation unit; performing keystone correction on an image to be
projected in accordance with the keystone correction amount; setting a
zero reference position, in which the keystone correction amount is zero,
within an operation range of the operation unit; setting a dead zone
within the operation range of the operation unit such that the dead zone
includes the zero reference position and an area surrounding the zero
reference position; and setting the keystone correction amount to zero in
accordance with the output value corresponding to the inside of the dead
zone.

9. The method according to claim 8, wherein the operation unit includes a
sliding or rotary variable resistor and an output voltage is changed
through the variable resistor in accordance with the operation amount,
and the keystone correction amount is set to zero in accordance with the
output voltage within a voltage range corresponding to the dead zone.

10. The method according to claim 8, wherein the projection display
apparatus further includes an image projecting unit, the operation unit
is a sliding operation device capable of being operated in a direction
orthogonal to a projection direction in which an image is projected by
the image projecting unit, and a keystone correction amount is set in the
direction orthogonal to the projection direction.

11. The method according to claim 8, wherein keystone correction is
performed while information regarding the keystone correction amount is
not provided to a user.

12. The method according to claim 8, wherein if the output value
corresponds to the inside of the dead zone, pixel interpolation is not
performed on the image, and if the output value corresponds to the
outside of the dead zone, pixel interpolation is performed on the image.

13. The method according to claim 8, wherein the operation unit provides
a click state at a specific operation position within the dead zone.

14. The method according to claim 13, wherein the operation unit provides
the click state at the zero reference position.

15. A projection display apparatus comprising: an image projecting unit
that projects an image; an operation unit, whose output value changes
depending on the amount of operation, that is a sliding operation device
capable of being operated in a direction orthogonal to a projection
direction in which the image is projected by the image projecting unit; a
correction amount setting unit that sets a keystone correction amount in
the direction orthogonal to the projection direction, and changes the
keystone correction amount in accordance with an output value of the
operation unit; and a keystone correcting unit that performs keystone
correction on an image to be projected in accordance with the keystone
correction amount.

Description:

[0002] The present invention relates to a projection display apparatus
capable of performing keystone correction and a method of controlling the
same.

BACKGROUND ART

[0003] Some projection display apparatuses (projectors) have a function
for keystone correction (trapezoidal distortion correction). The keystone
correction includes vertical keystone correction, as correction in the
top and bottom direction, and horizontal keystone correction, as
correction in the right and left direction. The projection display
apparatuses having the keystone correction function include a manual type
which is provided with two discrete rotary knobs to adjust the amount of
vertical keystone correction and the amount of horizontal keystone
correction in accordance with rotations of the rotary knobs (refer to PTL
1, for example).

CITATION LIST

Patent Literature

[0004] PTL 1: JP-A-2003-9038

SUMMARY OF INVENTION

Technical Problem

[0005] When the projection display apparatus is accurately disposed so as
to face a projection screen, horizontal keystone correction is not
needed. In this case, a user operates the rotary knob such that the
amount of horizontal keystone correction (hereinafter, "horizontal
keystone correction amount") is zero. Practically, however, it is
difficult to operate an analog operation device, such as a rotary knob,
to a single operation position where the amount of keystone correction
(hereinafter, "keystone correction amount") is zero. If the user has
intended to operate the rotary knob to such a zero position, the knob may
be actually deviated from the position slightly.

[0006] If the display apparatus is provided with a click mechanism to
generate a mechanical click state (a click and sense of clicking) at the
zero position where the keystone correction amount is zero, it is just
conceivable that the user may actually operate the rotary knob to a
position slightly deviated from the zero position though the user has
intended to operate the knob to the zero position. Simply adding the
click mechanism does not solve the difficulty of controlling the amount
of correction to zero.

[0007] If such an operation device includes a variable resistor, serving
as a relatively inexpensive part, such that the keystone correction
amount is set by a voltage value changed through the variable resistor,
individual variations between variable resistors result in variations in
voltage value. Each variable resistor therefore needs calibration.
Furthermore, a voltage value set by the variable resistor varies
depending on, for example, variation in power supply voltage or
temperature drift. In the use of the variable resistor, therefore, it is
more difficult to set a keystone correction amount to zero.

[0008] If the display apparatus is configured such that the current
keystone correction amount is indicated in a projected image, the user
can easily control the keystone correction amount to zero. Indication
processing is, however, required separately. Furthermore, since such an
indication overlaps part of the image which the user is viewing, it
hinders the viewing.

[0009] The present invention has been made in consideration of the
above-described circumstances. The present invention provides a
projection display apparatus in which a user can easily adjust the
keystone correction amount to zero without relying on an indication, and
a method of controlling the same.

Solution to Problem

[0010] An aspect of the present invention provides a projection display
apparatus including an image projecting unit that projects an image, an
operation unit whose output value changes depending on the amount of
operation, a correction amount setting unit that changes a keystone
correction amount in accordance with an output value of the operation
unit, and a keystone correcting unit that performs keystone correction on
an image to be projected in accordance with the keystone correction
amount, wherein a zero reference position in which the keystone
correction amount is zero is set within an operation range of the
operation unit, a dead zone, which includes the zero reference position
and an area surrounding the zero reference position, is set within the
operation range of the operation unit, and the correction amount setting
unit sets the keystone correction amount to zero in accordance with the
output value corresponding to the inside of the dead zone.

[0011] With this configuration, the dead zone including the zero reference
position of the operation unit and the area surrounding the zero
reference position is set within the operation range of the operation
unit and the keystone correction amount is set to zero in accordance with
the output value, corresponding to the inside of the dead zone, of the
operation unit. Accordingly, the user can easily set the keystone
correction amount to zero without relying on an indication of the
keystone correction amount.

[0012] In this aspect of the present invention, the keystone correction
amount may be easily set to zero using an inexpensive variable resistor.
Advantageously, the user can adjust the keystone correction amount
instinctively.

[0013] In this aspect of the present invention, the keystone correction
amount may be easily set to zero while information regarding the keystone
correction amount is not provided to the user.

[0014] In this aspect of the present invention, if the operation unit is
operated within the dead zone, pixel interpolation may be inhibited.
Advantageously, an input image can be displayed faithfully, thus
improving image quality.

[0015] In this aspect of the present invention, the operation unit may
reliably provide a click state within the dead zone. Accordingly, the
user can easily and reliably set the keystone correction amount to zero
without relying on vision. In this case, the operation unit may provide
the click state at the zero reference position. With this configuration,
the keystone correction amount can be more easily and reliably set to
zero.

[0016] Another aspect of the present invention provides a method of
controlling a projection display apparatus that projects an image, the
apparatus including an operation unit whose output value changes
depending on the amount of operation, the method including changing a
keystone correction amount in accordance with an output value of the
operation unit, performing keystone correction on an image to be
projected in accordance with the keystone correction amount, setting a
zero reference position, in which the keystone correction amount is zero,
within an operation range of the operation unit, setting a dead zone
within the operation range of the operation unit such that the dead zone
includes the zero reference position and an area surrounding the zero
reference position, and setting the keystone correction amount to zero in
accordance with the output value corresponding to the inside of the dead
zone.

[0017] With this configuration, the dead zone including the zero reference
position of the operation unit and the area surrounding the zero
reference position is set within the operation range of the operation
unit and the keystone correction amount is set to zero in accordance with
the output value, corresponding to the inside of the dead zone, of the
operation unit. Accordingly, the user can easily set the keystone
correction amount to zero without relying on an indication of the
keystone correction amount.

Advantageous Effects of Invention

[0018] Another aspect of the present invention provides a projection
display apparatus including an image projecting unit that projects an
image, an operation unit, whose output value changes depending on the
amount of operation, that is a sliding operation device capable of being
operated in a direction orthogonal to a projection direction in which the
image is projected by the image projecting unit, a correction amount
setting unit that sets a keystone correction amount in the direction
orthogonal to the projection direction, and changes the keystone
correction amount in accordance with an output value of the operation
unit; and a keystone correcting unit that performs keystone correction on
an image to be projected in accordance with the keystone correction
amount.

[0019] With this configuration, the user can adjust the keystone
correction amount instinctively.

[0020] According to the present invention, the user can easily set the
keystone correction amount without relying on an indication of the
keystone correction amount.

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a diagram illustrating a projector according to an
embodiment of the present invention.

[0022] FIG. 2A is a diagram explaining a case where the projector is
tilted in the top and bottom direction.

[0023] FIG. 2B is a diagram explaining a case where the projector is
tilted in the right and left direction.

[0024] FIG. 3 is a block diagram of the functional configuration of the
projector.

[0025] FIG. 4 is a graph illustrating of the relationship between a
keystone operation unit and a horizontal keystone correction amount.

[0026] FIG. 5 is a flowchart of an operation mode switching process.

[0027] FIG. 6A is a diagram explaining a non-adjustment mode.

[0028] FIG. 6B is a diagram explaining an adjustment mode.

[0029] FIG. 7 is a flowchart of control by a filter.

DESCRIPTION OF EMBODIMENT

[0030] An embodiment of the present invention will be described below with
reference to the drawings.

[0031] FIG. 1 illustrates a projector (projection display apparatus) 10
according to an embodiment of the present invention. The projector 10
projects image light representing an image to display an image (projected
image) PM on a screen SC, serving as a projection plane. The projector 10
has a keystone correction (trapezoidal distortion correction) function of
correcting a trapezoidal distortion of the projected image PM caused by
the relative positional relationship between the projector 10 and the
screen SC. The projected image PM may be either of a still image and a
moving image.

[0032] FIG. 2A is a diagram explaining a case where the projector 10 is
tilted in the top and bottom direction (also referred to as "the vertical
direction" or "the longitudinal direction"). Referring to FIG. 2A, the
optical axis OA of projected light is tilted in the top and bottom
direction relative to a normal NL of the screen SC by a tilt angle theta1
(hereinafter, referred to as a "vertical tilt angle theta1). If keystone
correction is not performed, a trapezoidally distorted projected image
PM1 is displayed such that the length of the upper side of the image
differs from that of the lower side as illustrated in left part of FIG.
2A. Right part of FIG. 2A illustrates a projected image PM11 subjected to
keystone correction in the top and bottom direction (vertical keystone
correction) for the vertical tilt angle theta1.

[0033] FIG. 2B is a diagram explaining a case where the projector 10 is
tilted in the right and left direction (also referred to as "the
horizontal direction" or "the lateral direction"). Referring to FIG. 2B,
the optical axis OA of projected light is tilted in the right and left
direction relative to the normal NL of the screen SC by a tilt angle
theta2 (hereinafter, referred to as the "horizontal tilt angle theta2").
If keystone correction is not performed, a trapezoidally distorted
projected image PM2 is displayed such that the length of the left side of
the image differs from that of the right side as illustrated in left part
of FIG. 2B. Right part of FIG. 2B illustrates a projected image PM22
subjected to keystone correction in the right and left direction
(horizontal keystone correction) for the horizontal tilt angle theta2.

[0034] Referring to FIG. 1, a housing 10A of the projector 10 is provided
with a keystone operation unit 12 disposed on the upper surface thereof
such that the keystone operation unit 12 can be operated in the right and
left direction (direction orthogonal to a projection direction). The
keystone operation unit 12 functions as a manual operation device for
horizontal keystone correction. The keystone operation unit 12 includes
an operation member 12A, which includes a sliding variable resistor and
which the user can slide horizontally while holding with fingers. When
the operation member 12A is operated from one side to the other side in a
sliding range, an output voltage changes in proportion to the amount of
operation (slide stroke) of the operation member 12A.

[0035] A constant power supply voltage V1 (3.3 V in the present
configuration) is applied to the keystone operation unit 12. An output
voltage changes depending on the position of the operation member 12A of
the keystone operation unit 12. In the present configuration, a
horizontal keystone correction amount is set on the basis of the output
voltage. Consequently, the horizontal keystone correction amount is set
by a user's manual operation.

[0036] In the present configuration, an operation direction for adjustment
of the horizontal keystone correction amount is allowed to coincide with
the right and left direction in which the optical axis OA is tilted and
horizontal keystone correction has to be performed. Accordingly, the user
can intuitively adjust the horizontal keystone correction amount and also
instinctively recognize the keystone operation unit 12 as an operation
unit for horizontal keystone correction amount.

[0038] The image processing unit 21 receives an image signal SA from an
external device 17, such as a personal computer or a DVD player,
connected thereto via a cable. The image processing unit 21 writes image
data corresponding to the signal SA to a frame buffer (not illustrated)
on a frame-by-frame basis, and performs IP conversion to convert the
image data from the interlace format to the progressive format,
resolution conversion to enlarge or reduce the size of the IP-converted
image data, and various color corrections to control, for example,
brightness and color saturation. The frame buffer stores original image
data output from the image processing unit 21, uncorrected image data
obtained by format-converting the original image data through the image
processing unit 21, and corrected image data obtained by performing
keystone correction on the uncorrected image data through the keystone
correcting unit 22.

[0039] The keystone correcting unit 22 corrects a trapezoidal distortion
caused when an image is projected while the projection axis
(corresponding to the optical axis OA of projected light) of the
projector 10 is tilted relative to the screen SC, namely, performs
vertical keystone correction and horizontal keystone correction. The
keystone correcting unit 22 includes a coordinate transformer 31 that
performs transformation of the coordinates for horizontal and/or vertical
keystone correction and a filter (pixel interpolator) 32 that performs
pixel interpolation associated with keystone correction.

[0040] To perform keystone correction, an image is displayed on the liquid
crystal display panel 24A such that the trapezoidal distortion is
compensated for. When keystone correction is typically performed in the
projector including the liquid crystal display panel, the liquid crystal
display panel 24A displays an image smaller than an original image to be
subjected to trapezoidal distortion correction. Fundamentally, the
original image is reduced. If the original image is angled significantly,
part of the image may be enlarged.

[0041] For reduction of the original image, simply thinning image data
results in a jagged image. The filter 32 performs pixel interpolation to
avoid jagged distortions. The filter 32 performs pixel interpolation on
the basis of a filtering coefficient associated with keystone correction.
The coordinate transformer 31 and the filter 32 may include a variety of
known components.

[0043] The image projecting unit 24 includes a light source device 25A
functioning as a light source, the liquid crystal display panel (also
termed a liquid crystal light valve) 24A, and a projection lens 25B. The
liquid crystal display panel 24A includes a transmissive liquid crystal
display panel including a plurality of pixels arranged in a matrix. The
liquid crystal display panel 24A is driven by the panel driving unit 23
such that the transmittance ratio of each pixel is changed to modulate
illumination light from the light source to image light representing an
image.

[0044] When the projector 10 is a 3-chip LCD projector, three liquid
crystal display panels 24A for the three colors of red, green, and blue
or RGB and mirrors and a prism for splitting light from the light source
device 25A and combining light are arranged. In the present embodiment,
the apparatus includes a single liquid crystal display panel 24A for the
convenience of description.

[0045] The projection lens 25B enlarges and projects image light modulated
by the liquid crystal display panel 24A. An optical system of the image
projecting unit 24 may include a lens array for adjusting light
distribution, a polarization adjusting element, a mirror, a dustproof
glass, and the like. The image projecting unit 24 may include a variety
of known components.

[0046] The sensor unit 26 functions as an angle detecting unit that
detects a tilt angle in the top and bottom direction (the vertical
direction or the longitudinal direction) of the projector 10, namely, the
vertical tilt angle theta1 illustrated in FIG. 2A. The sensor unit 26
includes a G-sensor (accelerometer) detecting the inclination of the
projector 10 with respect to the vertical direction, detects the vertical
tilt angle theta1 using the G-sensor, and transmits data indicating the
detected vertical tilt angle theta1 to the control unit 30.

[0047] The memory 27 stores various programs, such as a control program,
and various data items. The memory 27 further stores conversion data 27A,
which will be described later.

[0048] The control unit 30 reads the control program stored in the memory
27 and executes the program, thus functioning as a computer for
controlling the components of the projector 10.

[0049] Referring to FIG. 3, the projector 10 includes an analog-to-digital
(A/D) converter 33 that converts an output voltage, which is in analog
form, of the keystone operation unit 12 into digital form. A digital
value indicating the output voltage is transmitted as an operation output
value D1 from the A/D converter 33 to the control unit 30. The control
unit 30 functions as a correction amount setting unit that sets a
keystone correction amount on the basis of the operation output value D1.

[0050] In this case, the control unit 30 allows the keystone correcting
unit 22 to perform an automatic keystone correction process of
automatically performing vertical keystone correction on the basis of the
vertical tilt angle theta1 detected by the sensor unit 26 and a manual
keystone correction process of performing horizontal keystone correction
on the basis of the operation output value D1 associated with the
keystone operation unit 12.

[0051] The projector 10 is configured such that information regarding a
keystone correction amount (for example, the current value of the
keystone correction amount) is not provided to the user, so that the user
directs the projector 10 through the sliding keystone operation unit 12
to perform horizontal keystone correction without relying on an
indication. More specifically, the user operates the operation member 12A
of the keystone operation unit 12 from side to side within an operation
range to set a horizontal keystone correction amount in the range of -30
degrees to +30 degrees (one of the right and left ends is set to the
minus end and the other end is set to the plus end).

[0052] In this case, an equal assignment method may be used which sets a
point at the middle of the operation range to a zero position where the
horizontal keystone correction amount is zero, assigns a correction
amount of -30 degrees to one end of the operation range, assigns a
correction amount of +30 degrees to the other end, and equally assigns
correction amounts for horizontal keystone angles excluding -30 degrees,
0 degree, and +30 degrees, to operation positions between these ends.

[0053] According to this equal assignment method, however, it is difficult
for the user to operate the operation member 12A to the single middle
position where the keystone correction amount is zero. If the user has
intended to operate the operation member 12A to the zero position, the
operation member 12A may be deviated from the zero position. Such an
event will be called a first event alpha where the operation member 12A
is deviated from the zero position despite the user's intention.

[0054] For example, when the user accurately places the projector 10 such
that the horizontal tilt of the optical axis OA is zero, the user intends
to operate the operation member 12A to the zero position such that
horizontal keystone correction is not performed but the operation member
12A is slightly deviated from the zero position. In this case, horizontal
keystone correction is performed unnecessarily. It is therefore
preferable to avoid the first event alpha.

[0055] In addition, individual variations of the variable resistor in the
keystone operation unit 12, variation in the power supply voltage V1,
temperature drift, and noise are factors causing the first event alpha.

[0056] If the operation position of the operation member 12A of the
keystone operation unit 12 is not changed, the operation output value D1
may vary due to variation in the power supply voltage V1 applied to the
keystone operation unit 12, temperature drift, and/or noise. In this
case, an event in which the horizontal keystone correction amount is
changed despite the user's intention is caused. This event will be called
a second event beta where the horizontal keystone correction amount is
changed due to a factor other than operation. It is preferable to avoid
the second event beta.

[0057] The projector 10 with the present configuration has the following
countermeasures against the first event alpha and the second event beta.

Countermeasure Against First Event Alpha

[0058] According to this countermeasure, as illustrated in FIG. 4, the
middle position in the operation range, indicated at H, is set to a zero
reference position C where the horizontal keystone correction amount is
zero, and a continuous region CH (hereinafter, "central dead zone")
including the zero reference position C and an area surrounding the zero
reference position C is set to a zone where the horizontal keystone
correction amount is zero.

[0059] Specifically, the operation range H of the keystone operation unit
12 in this countermeasure is 0.1 m as illustrated in FIG. 4. An area
extending from the zero reference position C, which corresponds to the
middle position at a distance of 0.05 m from each end, to each side by a
distance of 0.01 m is the central dead zone CH. Accordingly, if the
operation member 12A is positioned within the central dead zone CH, the
horizontal keystone correction amount is set to zero (corresponding to a
horizontal keystone angle of 0 degree). For example, when the operation
member 12A is in a position indicated at (I) or (II) in FIG. 4, the
horizontal keystone correction amount is set to zero.

[0060] A region (left operation region LH in FIG. 4) between one end (left
end) of the central dead zone CH and one end (left end) of the operation
range H is allocated for adjustment of horizontal keystone correction
amounts of 0 to -30 degrees (up to a maximum horizontal keystone angle on
the one end).

[0061] In this region LH, as the operation member 12A moves to the one
end, the horizontal keystone correction amount continuously decreases. In
this countermeasure, the horizontal keystone correction amount decreases
in proportion to the movement of the operation member 12A toward the one
end in the region LH. For example, if the operation member 12A is in a
position (III) in FIG. 4, the horizontal keystone correction amount is
set to a correction amount of -15 degrees.

[0062] A region (right operation region RH in FIG. 4) between the other
end (right end) of the central dead zone CH and the other end (right end)
of the operation range H is allocated for adjustment of horizontal
keystone correction amounts of 0 to +30 degrees (up to a maximum
horizontal keystone angle on the other end).

[0063] In this region RH, as the operation member 12A moves to the other
end, the horizontal keystone correction amount continuously increases. In
this countermeasure, the horizontal keystone correction amount increases
in proportion to the movement of the operation member 12A to the other
end in the region RH. For example, if the operation member 12A is in a
position (IV) in FIG. 4, the horizontal keystone correction amount is set
to a correction amount of +20 degrees.

[0064] The above-described allocation is achieved by previously storing
the conversion data 27A (refer to FIG. 3) in table form, indicating the
relationship between the operation output value D1 of the keystone
operation unit 12 and the horizontal keystone correction amount, to the
memory 27. More specifically, the control unit 30 refers to the
conversion data 27A to determine a horizontal keystone correction amount
corresponding to the current operation output value D1, and controls the
keystone correcting unit 22. The conversion data 27A is not limited to
data in table form. The conversion data 27A may be information
(conversion data) indicating a relational expression indicating the
relationship in FIG. 4.

[0065] Consequently, if the user operates the operation member 12A such
that the operation member 12A enters the central dead zone CH, the
horizontal keystone correction amount can be set to zero. As compared
with a configuration in which the horizontal keystone correction amount
is set to zero at only the zero reference position C, the horizontal
keystone correction amount can be easily and reliably set to zero.

[0066] In this configuration, the operation direction for adjustment of
the horizontal keystone correction amount coincides with the right and
left direction, serving as the direction in which the optical axis OA is
tilted and horizontal keystone correction has to be performed.
Accordingly, the user can intuitively adjust the horizontal keystone
correction amount.

[0067] Furthermore, according to this countermeasure, the projector 10 is
provided with a click mechanism 41, schematically illustrated in FIG. 3,
which allows the keystone operation unit 12 to provide a mechanical click
state when the operation member 12A of the keystone operation unit 12 is
operated to the zero reference position C. The click mechanism 41 is a
mechanism which generates, for example, a sense of clicking and a click
using a spring material and a latching mechanism such that the user can
recognize a clicked position tactually and aurally. The click mechanism
41 may include a known mechanism.

[0068] Since this kind of click mechanism 41 is a mechanical component, a
position where the sense of clicking is generated varies depending on the
influence of an error, change over time, or the like.

[0069] In this configuration, in the use of the click mechanism 41, the
keystone operation unit 12 provides the click state at least in the
vicinity of the zero reference position C. In other words, the keystone
operation unit 12 reliably provides the click state within the central
dead zone CH. Accordingly, the user can reliably operate the operation
member 12A of the keystone operation unit 12 to the vicinity of the zero
reference position C, namely, into the central dead zone CH without
relying on vision. The user can therefore easily and reliably set the
horizontal keystone correction amount to zero while viewing an image
projected by the projector 10 in a dark room.

[0070] The central dead zone CH is allocated to an area of 20% of the
operation range H. If individual variations of the variable resistor in
the keystone operation unit 12, variation in the power supply voltage V1,
temperature drift, or noise occurs while the operation member 12A of the
keystone operation unit 12 is operated to the vicinity of the zero
reference position C, therefore, a variation in the operation output
value D1 is not beyond a voltage range, initially set, corresponding to
the central dead zone CH.

[0071] Accordingly, if individual variations of the variable resistor in
the keystone operation unit 12, variation in the power supply voltage,
temperature drift, or noise occurs, the horizontal keystone correction
amount can be held at zero.

[0072] The central dead zone CH is not limited to 20% of the operation
range H. The central dead zone CH may be below or above 20% of the
operation range H such that a variation in the operation output value D1
is not beyond the initial set range even when individual variations of
the variable resistor, variation in the power supply voltage V1,
temperature drift, or noise occurs. As described above, the
countermeasure against the first event alpha is provided.

Countermeasure Against Second Event Beta

[0073] According to this countermeasure, the projector 10 has, as
operation modes, an adjustment mode in which the keystone correction
amount is changed in accordance with an operation of the keystone
operation unit 12, i.e., the operation output value D1 as described above
and a non-adjustment mode in which the keystone correction amount is
fixed without depending on an operation of the keystone operation unit
12, i.e., the operation output value D1. The control unit 30 performs an
operation mode switching process.

[0074] FIG. 5 is a flowchart illustrating the operation mode switching
process. FIGS. 6A and 6B are diagrams explaining operations in these
modes. The operation mode switching process is repeated during turn-on of
the projector 10. The operation mode switching process may be stopped in
accordance with setting by the user.

[0075] As a precondition of the operation mode switching process, while
the keystone operation unit 12 is not operated for predetermined set time
(two seconds in this countermeasure) T0, namely, while the operation
output value D1 of the keystone operation unit 12 is not changed for the
set time T0 or more, the operation mode is switched to the non-adjustment
mode. Accordingly, if a state where the user does not operate the
keystone operation unit 12 continues, the operation mode is switched to
the non-adjustment mode. An operation in the non-adjustment mode will be
described below.

[0076] In the non-adjustment mode, the control unit 30 fixes the keystone
correction amount. In FIG. 6A, the horizontal keystone correction amount
is fixed to -15 degrees.

[0077] Referring to FIG. 5, in the non-adjustment mode, the control unit
30 detects an operation of the keystone operation unit 12 (step S1) to
determine whether an operation has been performed such that the operation
output value is beyond a predetermined region (step S2). This operation
means an operation performed such that the operation output value D1 is
beyond a continuous region (hereinafter, also referred to as the
"output-value-based dead zone") GH (refer to FIG. 6A) including the
operation output value D1 corresponding to the fixed keystone correction
amount and an area surrounding the output value. The output-value-based
dead zone GH is set such that a variation in the operation output value
D1 is not beyond the dead zone GH even if variation in the power supply
voltage V1, temperature drift, or noise occurs. The output-value-based
dead zone GH is set so as to include a variation range of the operation
output value D1.

[0078] For example, when a variation due to a factor (voltage variation,
temperature drift, or noise) other than operation is in the voltage range
of -0.2 V to +0.2 V, the dead zone GH is set to a variation range (of
-0.2 V to +0.2 V) in which the operation output value D1 is set to the
center value (reference).

[0079] More specifically, the control unit 30 detects the operation output
value D1 as processing in step S1 and determines, as processing in step
S2, whether the operation output value D1 is outside the
output-value-based dead zone GH. If the value is inside the
output-value-based dead zone GH (NO in step S2), the control unit 30
returns the process to step S1 and maintains the current operation mode,
i.e., the non-adjustment mode until the operation output value D1 is
beyond the output-value-based dead zone GH.

[0082] Subsequently, the control unit 30 determines whether the keystone
operation unit 12 has been operated within a predetermined period, i.e.,
the set time (two seconds in this countermeasure) T0 (step S6).
Specifically, the control unit 30 acquires the operation output value D1
of the keystone operation unit 12 at time intervals and determines on the
basis of the difference between the previous and following operation
output values D1 whether the keystone operation unit 12 has been
operated. If the keystone operation unit 12 has been operated (YES in
step S6), the control unit 30 returns the process to step S3 to continue
the keystone adjustment, namely, the adjustment mode.

[0083] FIG. 6B illustrates a case where a horizontal keystone correction
amount of -5 degrees is set in the adjustment mode. In the adjustment
mode, if the keystone operation unit 12 is operated, the horizontal
keystone correction amount is adjusted in accordance with the position of
the operation member 12A in steps S3 to S6. For example, when the
operation member 12A is positioned in an area corresponding to the
central dead zone CH, the horizontal keystone correction amount is set to
zero. When the operation member 12A is in the left end, the horizontal
keystone correction amount is set to -30 degrees. When the operation
member 12A is in the right end, the horizontal keystone correction amount
is set to +30 degrees.

[0084] Whereas, if the keystone operation unit 12 has not been operated
(NO in step S6), the control unit 30 finishes the operation mode
switching process. In this case, the fixed keystone correction amount is
kept, namely, the operation mode is switched to the non-adjustment mode.
At the completion of processing in step S6, the operation mode switching
process is restarted from step S1 immediately or in accordance with an
interruption signal output at predetermined interruption intervals. Thus,
if an operation has been performed such that the operation output value
D1 is beyond the predetermined region in the non-adjustment mode (YES in
step S2), the operation mode is switched to the adjustment mode, such
that keystone correction can be performed.

[0085] As described above, if the keystone operation unit 12 has not been
operated in the adjustment mode, the operation mode is switched to the
non-adjustment mode in which the keystone correction amount is fixed.
Even when the operation output value D1 varies due to a factor (variation
in the power supply voltage V1, temperature drift, or noise) other than
operation, such an event that the keystone correction amount is changed
can be avoided. As described above, the countermeasure against the second
event beta is provided.

[0086] In some cases, the output-value-based dead zone (first dead zone)
GH, which is set in the non-adjustment mode, overlaps the central dead
zone (second dead zone) CH. In this case, if the operation output value
D1 enters the central dead zone CH because of a factor (voltage
variation, temperature drift, or noise) other than operation and the
keystone correction amount is adjusted to zero, an even in which the
keystone correction amount varies due to the factor other than operation.

[0087] According to this countermeasure, in order to avoid such an event,
when the operation output value D1 is inside the central dead zone CH in
the adjustment mode, the keystone correction amount is adjusted to zero.
When the operation output value D1 is inside the central dead zone CH in
the non-adjustment mode, the control unit 30 fixes the keystone
correction amount on the basis of the conversion data 27A without setting
the keystone correction amount to zero.

[0088] Accordingly, in the case where the operation output value D1 is
inside the output-value-based dead zone (first dead zone) GH and is also
inside the central dead zone (second dead zone) CH, the keystone
correction amount is fixed in the non-adjustment mode. In the adjustment
mode, the keystone correction amount is adjusted to zero. Consequently,
the event in which the keystone correction amount is adjusted to zero
when the operation output value D1 enters the central dead zone CH
because of a factor other than operation can be avoided.

[0089] Control by the filter 32 will now be described. The filter 32 has a
function of calculating a filtering coefficient for pixel interpolation
and performing pixel interpolation based on the filtering coefficient
under the control of the control unit 30.

[0090] FIG. 7 is a flowchart of a control process of the filter 32. The
control process is performed when vertical keystone correction is not
performed. Referring to FIG. 7, when the operation mode is the adjustment
mode (YES in step S11), the control unit 30 determines whether the
keystone operation unit 12 has been operated outside the central dead
zone CH (step S12). In the non-adjustment mode (NO in step S11), the
control unit 30 terminates the process and again performs the process
immediately or in accordance with an interruption signal output at
predetermined interruption intervals.

[0091] When determining in step S12 that an operation has been performed
outside the central dead zone CH (YES in step S12), the control unit 30
allows the filter 32 to calculate a filtering coefficient for pixel
interpolation in accordance with a horizontal keystone correction amount
and perform pixel interpolation (step S13). Thus, pixel interpolation for
horizontal keystone correction is performed.

[0092] Whereas, if an operation has been performed within the central dead
zone CH (NO in step S12), the control unit 30 allows the filter 32 to set
a filtering coefficient to zero (step S14). When a filtering coefficient
of zero is set, an input of the filter 32 agrees with an output thereof.
Accordingly, filtering is not performed. In other words, pixel
interpolation is not performed (pixel interpolation is inhibited).

[0093] In the present configuration, therefore, when an operation has been
performed within the central dead zone CH, pixel interpolation can be
inhibited while an image data processing path is not changed. When
vertical keystone correction is performed, this process is not carried
out and pixel interpolation according to vertical and horizontal keystone
corrections is performed. In some cases, pixel interpolation reduces
jagged distortions of an image but causes the image to be blurred. In the
present configuration, when an operation has been performed within the
central dead zone CH, pixel interpolation is inhibited. Accordingly, an
input image can be faithfully displayed, thus improving image quality.

[0094] As described above, in the present configuration, the control unit
30 sets the central dead zone CH including the zero reference position C,
serving as a single point within the operation range of the keystone
operation unit 12, and sets the horizontal keystone correction amount to
zero in accordance with the operation output value D1 corresponding to
the inside of the central dead zone CH. Advantageously, the user can set
the horizontal keystone correction amount to zero without relying on an
indication of the horizontal keystone correction amount.

[0095] The keystone operation unit 12 includes a sliding variable resistor
and allows the variable resistor to change the operation output value D1
in accordance with the amount of operation. The control unit 30 sets the
horizontal keystone correction amount to zero in accordance with the
operation output value D1 within a voltage range corresponding to the
central dead zone CH. Advantageously, the horizontal keystone correction
amount can be easily set to zero using the variable resistor which is
inexpensive. In the use of the variable resistor, the operation output
value D1 varies due to individual variations of the resistor, voltage
variation, temperature drift, or noise. If the operation output value D1
varies, however, the variation is inside the central dead zone CH.
Advantageously, an event in which the horizontal keystone correction
amount changes from zero to another value despite user's intention can be
avoided.

[0096] The keystone operation unit 12 is slidable in the direction
orthogonal to the projection direction in which an image is projected by
the image projecting unit 24. Since the user operates the keystone
operation unit 12 to adjust a horizontal keystone correction amount in
the direction orthogonal to the projection direction, the user can adjust
the horizontal keystone correction amount intuitively. Furthermore, the
user can instinctively recognize the keystone operation unit 12 as an
operation unit for horizontal keystone correction. In addition, since the
keystone operation unit 12 provides a click state at the zero reference
position C, serving as a specific operation position within the central
dead zone CH, the click state can be ensured within the central dead zone
CH using the mechanical click mechanism. Thus, the user can easily and
reliably set the horizontal keystone correction amount to zero without
relying on vision.

[0097] When the operation output value D1 of the keystone operation unit
12 is inside the central dead zone CH, the filter 32 does not perform
pixel interpolation. Accordingly, when an operation is performed within
the central dead zone CH, pixel interpolation can be inhibited. An input
image can be therefore displayed faithfully, thus improving image
quality.

[0098] In the present configuration, in the adjustment mode in which the
horizontal keystone correction amount is varied in accordance with the
operation output value D1 of the keystone operation unit 12, the control
unit 30 monitors the operation output value D1 to determine whether the
keystone operation unit 12 has not been operated. If the keystone
operation unit 12 has not been operated, the control unit 30 switches the
operation mode to the non-adjustment mode in which the horizontal
keystone correction amount is fixed. Advantageously, an event in which
the horizontal keystone correction amount varies due to a factor (voltage
variation, temperature drift, or noise) other than a user's operation can
be avoided.

[0099] Particularly, in the present configuration, the keystone operation
unit 12 includes the variable resistor whose output value tends to vary
due to voltage variation, temperature drift, or noise. The variation of
the variable resistor can be adequately avoided. While the inexpensive
variable resistor is used, therefore, the event in which the horizontal
keystone correction amount changes due to a factor other than a user's
operation can be avoided.

[0100] In the present configuration, since keystone correction amount
information is not provided to the user, an event in which the user does
not notice a change in keystone correction amount caused by a factor
other than operation may occur. The present invention can, however, avoid
such an event. In other words, the present invention is suitable for a
configuration in which keystone correction amount information is not
provided to the user.

[0101] In the present configuration, in the non-adjustment mode, the
control unit 30 sets the output-value-based dead zone (first dead zone)
GH including the variation range of the operation output value D1. While
the operation output value D1 is inside the output-value-based dead zone
GH, the horizontal keystone correction amount is fixed. When the
operation output value D1 is outside the output-value-based dead zone GH,
the operation mode is switched to the adjustment mode. While an event in
which the horizontal keystone correction amount changes due to a factor
other than a user's operation is avoided, the horizontal keystone
correction amount can be adjusted in accordance with a user's operation,
thus improving ease of use.

[0102] The output-value-based dead zone GH is set on the basis of the
operation output value D1 obtained when the operation mode is switched to
the non-adjustment mode. Accordingly, a proper dead zone can be set such
that the horizontal keystone correction amount is not changed if the
operation output value D1 varies due to a factor other than an operation
upon switching.

[0103] In the case where the operation output value D1 is inside the
output-value-based dead zone GH and is also inside the central dead zone
(second dead zone) CH, the control unit 30 fixes the horizontal keystone
correction amount in the non-adjustment mode. In the adjustment mode, the
control unit 30 sets the horizontal keystone correction amount to zero.
While the keystone correction amount can be easily set to zero in the
adjustment mode, therefore, an event in which the horizontal keystone
correction amount is adjusted to zero if the operation output value D1
enters the central dead zone CH because of a factor other than operation
can be prevented.

[0104] The above-described embodiment is intended to merely describe an
embodiment of the present invention. Any modifications and applications
can be made without departing from the spirit of the present invention.

[0105] For example, in the above-described embodiment, the present
invention is applied to horizontal keystone correction. The present
invention can be applied to vertical keystone correction. The present
invention can be applied widely to known keystone correction.

[0106] In the above-described embodiment, the keystone operation unit 12
includes the sliding variable resistor. The present invention is not
limited to the embodiment. The keystone operation unit 12 may include a
rotary variable resistor or an operation device other than a variable
resistor.

[0107] In the above-described embodiment, the keystone operation unit 12
provides a click state when operated to the zero reference position C.
The present invention is not limited to the embodiment. The keystone
operation unit 12 may provide a click state in a specific operation
position other than the zero reference position C.

[0108] The above-described functional units, e.g., the image processing
unit 21, the keystone correcting unit 22, and the control unit 30 serve
as functional components of the projector 10. Concrete forms of them are
not especially limited. In other words, hardware corresponding to each
functional unit does not always have to be installed. A single processor
may perform a program to realize functions of a plurality of functional
units.

[0109] The above-described projector 10 is of the type in which an image
is projected onto the screen SC using the transmissive liquid crystal
display panel 24A. A projector with a reflective liquid crystal display
panel may be used. Alternatively, a DMD projector with a digital
micromirror device may be used. In addition to the 3-chip LCD projector
that projects a color image using three light valves, the present
invention can be applied to a projector that displays images
corresponding RGB using a single liquid crystal light valve in a
time-division manner to project a color image, a single-chip DMD
projector including a color wheel, and a 3-chip DMD projector. As regards
the light source, any of various light sources, such as a xenon lamp, an
ultra-high pressure mercury lamp, an LED lamp, may be used. The
above-described projector 10 may be of the type which is disposed on the
front side of the projection plane and projects projection light to the
front surface of the projection plane. Alternatively, the projector 10
may be of the type which is disposed on the rear side of the projection
plane and projects projection light to the rear surface of the projection
plane. In other words, the present invention can be applied widely to
projection display apparatuses having a function of modulating light
emitted from a light source.

[0110] In the present embodiment, the image signal SA is supplied from the
external device 17 to the projector 10. For example, the projector 10 may
include a reading device that reads data from an external recording
medium, such as an optical disk or a flash memory, and the reading device
may read data stored in the recording medium to acquire the image signal
SA.